EINTR是linux中函数的返回状态，在不同的函数中意义不同。表示某种阻塞的操作，被接收到的信号中断，造成的一种错误返回值。
write
表示：由于信号中断，没写成功任何数据。
The call was interrupted by a signal before any data was written.
read
表示：由于信号中断，没读到任何数据。
The call was interrupted by a signal before any data was read.
sem
sem_wait
函数调用被信号处理函数中断
The call was interrupted by a signal handler.
recv
由于信号中断返回，没有任何数据可用。
function was interrupted by a signal that was caught, before any data was available.